‘81 Failed Smog - Running Lean - Probable Causes?

[maxm50]

Hi all,
I’ve found a beautiful 1981 (fuel injected) spider for sale locally that I’m interested in. The seller just smogged it and it failed - the smog tech said it was “running lean”.

I am debating between letting the seller fix it or offering him a lower price to buy it without a smog cert, and fix it myself. My past experience says the most likely cause of an old fuel injected engine running lean enough to fail smog but not so lean as to be undrivable is a small crack or leak in the intake tract after the airflow meter. But, I don’t have specific experience with Fiat engines yet.

My question is: if you were investigating a fuel injected spider that’s running lean, what would you look at as a likely cause? My gut says it’s probably something simple like an air leak, but I’d like to know if it’s common for something more serious to go wrong on these cars and cause lean running (ie faulty injectors, faulty ECU, faulty airflow meter, etc)

Thank you!
-Max

[18Fiatsandcounting]

Does the seller have the actual test results from the smog check, that he could share with you (NOx, hydrocarbons, CO, residual oxygen, etc)? "Running lean" could point to a whole lot of potential causes, so it's going to be hard to pin down the problem with only that info.

-Bryan

[SteinOnkel]

"I am debating between letting the seller fix it or offering him a lower price to buy it without a smog cert, and fix it myself."

The seller would be an absolute fool to let you do this. Thanks to our wonky laws regarding smog, the seller is on the hook unless he can provide a valid smog certificate. There's already been court cases in which the seller was stuck with the bill of fixing a car he didn't even own anymore.

I would stay well away from a 39 year old fuel injected car that just failed smog. It could be anything.

[MattVAS]

It could be a lot of things, but due to the reliability of the FI cars I bet is it regular maintenance that hasn't been done.
Oxygen Sensor probably is the original
Temp Sensor for the ECU
Both those can be bad (or badish) and allow the car to still be drivable.

Could also be the wrong spark plugs ask if they are recently replaced and what type exactly they are.
Could be the catalytic convertor is totally trashed, week ignition coil (news flash they don't last 39 years), and maybe bad injectors.

Also, since you haven't seen the report on how it ran I wouldn't just believe it was lean. The tech may just say that by default to make people leave. Those guys don't care they just want to do the next car in line.

[maxm50]

Excellent feedback, thanks guys. I'll see if I can get a photo of the smog results from the seller and reply back.

[maxm50]

Hi all,
The seller was able to find the smog test papers. Here are the results below.
HC and CO are well within the limits, but NO is really high. Is anyone skilled in using these results to point out any probable causes for the failure? I did learn that the catalytic converter is only a year old on this car. So, there goes one easy fix .

Thanks!

15mph:
%CO2: 14.8
%O2: 0.7
HC (PPM): 17 (Limits: Max 152, Gross Polluter 342)
CO (%): 0.00 (Limits Max 1.05, Gross Polluter 2.55)
NO (PPM): 3082 (Limits: Max 1191, Gross Polluter 2331)

25mph:
%CO2: 14.9
%O2: 0.6
HC (PPM): 12 (Limits: Max 123, Gross Polluter 274)
CO (%): 0.00 (Limits Max 0.85, Gross Polluter 2.35)
NO (PPM): 3108 (Limits: Max 1021, Gross Polluter 2131)

[SteinOnkel]

https://www.smogtips.com/failed-high-NO ... -oxide.cfm

[18Fiatsandcounting]

In addition to the items mentioned in the website from Steiny above, one other cause of high NOx is a leak in the exhaust manifold, header, downpipe, whatever you have. In particular, a leak BEFORE the catalytic converter. Given that the catalytic converter was replaced, I suggest checking the tightness of the connections at the front, and all connections between there and the engine. Sometimes there's a metal doughnut in the front catalytic converter connection, and that could also be deformed/missing/leaking. Also the doughnut or gasket between the exhaust manifold and downpipe, or the exhaust manifold flange and gasket.

The exhaust stream "pulses" as the valves open and close, and while this normally pushes exhaust out of the pipes, air can also be sucked into the pipe in between those pulses. That outside air (essentially oxygen and nitrogen), when it runs through the super hot catalytic converter, forms NOx.

I actually saw this on my '93 Jag XJ6 a few years ago. I replaced the catalytic converter as the HC emissions had crept up over the years, and the new catalytic converter solved that. But, I didn't tighten the front connector enough, so the NOx emissions went way up From 5 ppm to 500 ppm. Tightening the front connection to the converter solved that problem.

The good news is that, since the HC and CO numbers are really low, you're getting complete combustion and so it's likely not an air/fuel ratio issue. Based on what you've described, it's probably an exhaust leak as I mentioned above, or a fault in the EGR system.

EDIT: I do realize the car isn't yours to play around with, but this gives you some ideas as to what you might be facing if you bought the car.

-Bryan

[maxm50]

Hi Brian,
This is exactly the kind of info I was looking for. Makes perfect sense to me. Glad to know that the HC/CO numbers indicate complete combustion - that's great news and rules out most of the things I was thinking of.

I'm not sure yet if I'll need to buy it without a smog cert (not sure about much of anything in this weird time right now), but if it comes down to that, this "point me in the right direction" from you is very, very helpful. Thank you! I'll let you know how it goes.
Hopefully if all goes well I'll be joining your ranks soon!

Cheers,
Max

[maxm50]

I just wanted to conclude this thread in case it helps others in the future:

Bryan was 100% right. I had massive exhaust leaks just upstream of the cat. The PO's shop had WELDED the cat to the downpipe flange (probably because they didn't have a 4-bolt flange laying around, not surprising). And they did a terrible job. I put some soapy water on the welds and then started the car, and it bubbled and foamed a hilarious amount.

I had a local shop cut it off and weld on a modern 3-bolt flange to the end of the downpipe and to the cat, mate them up, and clean up some other nasty welds around the cat. They did a beautiful job. Would've loved to keep the 4-bolt flange, but it was too mangled to salvage without removing the whole downpipe from the car.

Today I took the car to get smogged again and it passed with plenty of headroom!

So, to any future readers, heed Bryan's advice above if you have high NOx numbers.

[18Fiatsandcounting]

Glad I could be of help, but of course this means my next 5 suggestions will be wrong. Reversion to the mean, that sort of thing.

-Bryan